Power transmission



Oct. 17, 1950 H. E. NIXON 2,525,934

POWER musuxssxou 1mm April 11, 1946 IN V EN TOR.

HARLEY E. NIXON ATTORNEY Patented Oct. 17, 1950 rowan TRANSMISSION Harley E. Nixon, Detroit, Mich, assignor to Vickers Incorporated, Detroit, Mich., a corporation of Michigan Application April 11, 1946, Serial No. 661,235

12 Claims.

This invention relates to power transmissions, particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

Closed hydraulic transmission circuits are constantly subjected to loss of hydraulic operating fluid, either as a result of leakage or due to relieving the circuit of excess pressure. To replace that loss of fluid, it is standard practice to employ a separate means such as a replenishing pump. The leakage and excess pressure'fluid is drained to a collection reservoir where it is picked up by the replenishing pump and forced back into the transmission at circuit pressure. i

The general object of this invention is to provide a piston type pump adapted to take part of its hydraulic fluid supply from one source and part from another. In other words, the proposed pump cylinders during suction stroke will be initially supplied from one pressure fluid source and finally filled from another source.

One of the objects of this invention is to provide a design of the operating pump for a closed transmission circuit adapted to perform a secondary function, namely, that of replenishing the transmission circuit. By eliminating the necessity of a separate replenishing pump, an economic saving not only in the original investment but also in the efliciency and maintenance is realized.

This invention particularly applies topumps of the type employing a casing in which a cylinder barrel is rotatably mounted and provided with a plurality of axiall disposed cylinders and pistons reciprocably mounted therein and a valve for porting the fluid to and away from the cylinder. In order to adapt this type of pump to the dual purpose of power transmission and replenishing, novel valving and porting are necessary.

Consequently, a valve and cooperating passages have been developed, whereby fluid may be supplied to the pump from two independent sources at diflerent pressures. Therefore, another object of this invention is to provide a valve and connecting passages for independently handling the pressure fluid from two sources of supply maintained at difl'erent pressures.

A further object is to design a valve employing two inlet ports adapted to communicate with the pump cylinder during selected portions of the suction stroke. valve will port the low pressure fluid supply to the cylinders during the earl part of the suction stroke. By deduction, it is evident that the higher pressure fluid supply will be employed to In other words, the proposed tlll any voids remaining after the initial filling of the cylinders.

In order to design an efllclent pump for the proposed dual purpose, the length and position of the valve ports are important. The speed of the pump must also be taken into account dur ing the calculation. Consequently, the inlet ports must be made as long as possible within the limits of preventing intercommunicating flow between the ports at normal operating speed. Therefore, a further object of this invention is to provide a valve plate design adapted to produce maximum inlet portage but, at the same time, prevent any flow between the inlet ports at normal operating speed.

The proposed pump design has a special application and advantage in aircraft hydraulic transmissions. High altitude flying imposes difflculties with open circuits due to the possible suction failure and resulting in pump cavitation. To overcome cavitation resulting from low absolute pressure in the suction line, it is standard practice to provide separate means for supercharging the pump suction. In the proposed device, the main delivery pump also performs the function of a supercharger.

Therefore, another object of this invention is to provide a pump capable of supercharglng its atmospheric suctionvolume and filling the cavities resulting from high altitude operation. In order for a pump to perform that double purpose, it is necessary that part of the operation be devoted to supercharglng and the balance to its normal functioning as a pump. To correctly divide the functions, it is necessary to control the pump cycle by a novel valve.

Therefore, the general object of this invention is to provide a pump and special valve provided with ports of a correct size and position whereby the pump can be supplied by two independent fluid sources of different pressures.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

Figure l is a transmission circuit including a pump employing a preferred form of the invention.

Figure 2 is a plan view of the valve plate showing the inlet and outlet ports.

In detail, Figure 1 illustrates a pump in connected to a motor I2 by means of the pressure conduit H and return conduit [6. A pressure relief valve H3 in the pressure conduit I4 drains through conduit 28 to the return conduit i 6. Relief valve 22 in the return conduit l6 drains through conduit 24 to tank 26. The suction conduit 28 extends from the tank 26 to the pump. I8. A four-way valve 38 in the pressure conduit l4 ports pressure fluid through motor conduits 82 and 34 to motor I2. The motor I2 is provided with two cylinder chambers 36 and 38 and a double acting piston 48 mounted on the rod 42.

The pump I8 is provided with a plate valve 44 having two inlet ports 46 and 48 and an outlet port 58. A circular recess 52 is connected by drain passages 54 and 56 to the pump case 58. Inlet port 46 extends clear through valve plate 44, but inlet port 48 is a recess in the surface and substantially wider than inlet port 46. Inlet port 48 is adapted to communicate with cylinder 68 by means of cylinder ports 6| and passages 62, and directly with the case 68 of pump ID as illustrated in Figure 1. The return line I6 is fastened to the case 58 by fittings 64, the suction conduit 28 by fitting 66, and the pressure conduit l4 by fitting 68. The cylinder barrel [8 is provided with a plurality of cylinders 68 with pistons 12 reciprocably mounted therein and is driven by a prime mover (not shown) through shaft 14.

In operation, fluid at atmospheric pressure is supplied from the tank 26 through suction conduit 28 and fitting 66 to the pump l8, where it is conducted to the cylinders 68 by means of the first or initial suction port 46 of valve plate 44. The pump delivery or discharge is ported through the outlet port 58 to fitting 68 and into the pressure conduit l4.

Operating pressure fluid passes through conduit l4 to the four-way valve 38 for controlling the direct onal flow through conduits 32 and 34 of the motor i2. Discharge fluid from the motor I2 and four-way valve 38 enters return conduit l6 through which pressure fluid may be transmitted to pump l8 or to tank 26 via relief valve 22. In case the motor i 2 is blocked, the

relief 18 will open at its maximum operating pressure setting and permit the excess pressure fluid to flow through conduit 28 to the return line 16, thereby by-passing the motor l2.

Relief valve 22 is set at a pressure substantially above atmospheric. as for example, fifty pounds per square inch. Therefore, the pressure in return conduit l6 will be maintained at a predetermined fleure and ret rn flow thro gh fltting 64 and inlet port 48 will enter the cylinders supercharged at fifty pounds per scuare inch above atmospheric. The path of flow of the supercharged pre sure flu d enters the pump casing 58 through fitt ng 64 and thence'contnues between the casing bore and the cylinder barrel 18 directly into the shallow recess inlet port 48 which is substantially wider than the atmospheric pressure inlet port 46. From port 48, inlet pressure fluid enters the cylinder 68 through the cylinder ports 6| and passages 62 in the barrel 18.

It will thus be seen that pump I8 is provided with dual suction means, each connected indel pendently to different pressure fluid so rces."

ing of the void through supercharging. Another basic use of the invention is as a replenishing pump wherein a closed circuit return line is connected to port 48 and a tank suction line is connected to port 46.

The valve plate design shown in Figure 2 illustrates the discharge or outlet port 68 and the two inlet ports 46 and 48. The separation or land between the inlet ports is provided oi a length in proportion to the difference in pressure between the ports and indirectly proportioned t0 the speed of the cylinder barrel thus preventing intercommunicating flow between ports at normal operating speeds and pressures. The lengths oi inlet ports 46 and 48 are designed with reference to the rate of fluid flow and piston travel in the cylinders. In other words, the rate. of piston travel during suction stroke increases to its midpoint of travel. Due to the inertia of the hydraulic fluid flow a difference in phase exists between the varying rate of piston travel and the changing fluid velocity, whereby the variable fluid velocity lags the piston travel rate. Therefore, to exert maximum suction on the inlet port connected to the atmospheric pressure fluid, the cutoff or porting should follow immediately after the piston has passed its maximum rate of travel, or in other words, when the fluid flow rate has reached its maximum value.

' Many combinations and variations of the inlet ports can be provided for modified purposes. It may be desirable to employ several independent pressure fluid supply sources and a plurality of independent valve inlet ports for varying purposes including combinations of atmospheric and pressure supplies, replenishing and supercharging features, and the filling of voids or eliminating of cavitation. Many modifications are possible by mere y varying the size, position. and number of the inlet ports or the spacing between them.

In Figure 2, the inlet ports 46 and 48 are shown separated by a narrow land. In the same figure, a cylind r barrel port 6| is represented by dotted lines. It is evident from the illustration that each cylinder port 6i establishes intercommunication between the inlet ports for a short interval of time during each revolution. It would, therefore, appear that supercharged fluid entering the cylinder 68 through the valve inlet port 48 will also enter the atmospheric pressure port 46.

Whether or not an intercommunicating flow between the inlet ports 46 and 48 via cylinder port 6| does actually take place is not known. The speed of the pump coupled with the fluid inertia apparently prevents this flow as far as experim nts have shown; However, it has been proven that a pump employing double inlet port valves illustrated as compared with a conventional single in'et port valve produces greater delivery and higher overall efliciency. This is especially true at higher altitudes where lower atmospheric pressure exists.

It will thusbe seen that the present invention has provided a pump adapted to operate a transmission circuit and at the same time supercharge or replenish that circuit and receive pressure fluid from two independent sources of supply during normal operation. This is accomplished by the use of a novel pump and valve design tomodify or change the present method of introducing suction fluid into the pump cylinders and eliminating cavitation.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. A valve for a fluid pressure energy translating device employing two sources of hydraulic pressure fluid at different pressures and a casing housing a revolving cylinder barrel containing a plurality of cylinders and pistons reciprocable therein, including an outlet port in the valve plate adapted to communicate with the cylinders during the compression stroke of the pistons, and two inlet ports the first being connected to the lower pressure fluid source and adapted to communicate with the cylinders during the first part of the suction stroke up to the momentimmediately following the point where the pistons "attain their maximum rate of suction travel, and a second arcuate inlet port connected to the higher pressure fluid source and adapted to communicate with the cylinders during the remainder of the suction stroke.

2. A valve for a fluid pressure energy translating device employing two sources of hydraulic pressure fluid at different pressures and a casing housing a revolving cylinder barrel containing a plurality of cylinders and pistons reciprocable therein, including an outlet port in the valve plate adapted to communicate with the cylinders during the compression stroke of the pistons, and

two inlet ports the first being connected to the lower pressure fluid source and adapted to com municate with the cylinders during the first part of the suction stroke and a second arcuate inlet port connected to the higher pressure fluid source and adapted to communicate with the cylinders immediately following the moment when the pistons have reached their maximum velocity during the suction stroke and during the remainder of the suction stroke.

3. A valve for a fluid pressure energy translating device employing two sources of hydraulic pressure fluid at different pressures and a casing housing a revolving cylinder barrel containing a plurality of cylinders and pistons reciprocable therein, including an outlet port in the valve plate adapted to communicate with the cylinders during the compression stroke of the pistons, and two inlet ports the first being connected to the lower pressure fluid source and adapted to communicate with the cylinders during the first part of the suction stroke, and a second arcuate inlet port connected to the higher pressure fluid source and adapted to communicate with the cylinders when the fluid flow in the cylinders from the first inlet port has reached its maximum velocity and during the remainder of the suction stroke.

4. In a fluid pressure energy translating device of the type having a casing member, a driving member, and a valve including an inlet port connected to an atmospheric pressure fluid source and adapted to partially flll each cylinder during the early portion of its suction stroke, and a, second independent inlet port connected to a hydraulic fluid source maintained at a pressure substantially above atmospheric pressure and 0 adapted to fill the additional suction cylinder displacement developed during the balance of the suction stroke as well as any voids left during the initial filling from the atmospheric pressure the early portion of its suction stroke, and a second independent inlet port connected to a supercharged pressure fluid source and adapted to admit the supercharged pressure fluid into the cylinder cavities during the latter part of the suction stroke thereby filling all voids and preventing cavitation.

6. For use in a hydraulic power transmission system having an atmospheric pressure fluid source and a supercharged pressure fluid source, a fluid energy translating device of the type havmg a casing housing a revolving cylinder barrel with a plurality of axially disposed cylinders and pistons reciprocable therein and a valve including two independent inlet ports, one of which connects the atmospheric pressure fluid source to the cylinders during the initial portion of the suction stroke, and the other of which connects the supercharged pressure fluid source to the cylinders during the remainder of the suction stroke.

7. For use in a hydraulic power transmission system having an atmospheric pressure fluid source and a supercharged pressure fluid source, a fluid energy translating device of the type havmg acasing housing a revolving cylinder barrel with a plurality of axially disposed cylinders and pistons reciprocable therein and a valve includ ing an outlet port and two independent inlet ports, the outlet port communicating with the cylinders duringthe compression stroke of the pistons, one of the inlet ports connecting the atmospheric pressure fluid source to the cylinders during the initial portion of the suction stroke of the pistons for initiallyfllling the cylinders, and the other inlet port connecting the supercharged pressure fluid source to the cylinders during the remainder of the suction stroke for injecting pressure fluid into the cylinders at supercharged pressure and completely filling the same, thereby preventing cavitation.

8. For use in a hydraulic power transmission system having an atmospheric pressure fluid source and a supercharged pressure fluid source, a fluid energy translating device of the type havmg a casing housing a revolving cylinder barrel with a plurality of axially disposed cylinders and pistons reciprocable therein and a valve including two independent inlet ports, one of which connects the atmospheric pressure fluid source to the cylinders during the initial portion of the suction stroke while the replenishing fluid flow through the inlet port is increasing to its maximum velocity, and the other of which connects the supercharged pressure fluid source to the cylinders immediately following the close of the first inlet port and. during the remainder of the suction stroke for completely filling the cylinders with supercharged pressure fluid and preventing cavitation.

9. For use in a hydraulic power transmission system having an atmospheric pressure fluid source and a supercharged pressure fluid source, a fluid energy translating device of the type having a casing provided with two inlet ports adapted to be independently connected to the pressure flud sources and an outlet port, said casing housing a revolving cylinder barrel with a plurality 'of axia ly disposed cylinders and pistons reciprocable therein, and a valve including an outlet port and two independent inlet ports, the former of which is connected to the casing outlet port and the latter of which are independently connected to the casing inlet ports, one of which connects the atmospheric pressure fluid source aszspac to the cylinders during the initial portion of the suction stroke and the other of which connects the supercharged pressure fluid source to the cylinders during the remainder of the suction stroke.

10. In combination a fluid pump of the type having a casing housing a revolving cylinder barrel with a. plurality of axially disposed cylinders having pistons reciprocable therein, and a valve having an outlet port and two independent inlet ports, the first inlet port being connected to the cylinders during the initial suction stroke of the pistons and the second of which is connected to the cylinders during the remainder of the suction stroke, a source of fluid at atmospheric pressure connected to the first inlet port, a fluid motor, separate conduit means connecting the pump outlet port to the motor inlet and the motor outlet to the pump second inlet port, means for maintaining a predetermined supercharged pressure in the conduit connecting the motor outlet to the pump second inlet port for injecting pressure fluid into the cylinders at a supercharged pressure during the remainder of the suction stroke of the pistons thereby preventing cavitation, and means for exhausting excessive pressure fiuid not needed by the cylinders.

11. In combination a fluid pump of the type having a casing provided with first and second inlet ports and an outlet port, said casing housing a revolving cylinder barrel with a plurality of axially disposed cylinders having pistons reciprocable therein and a valve having an outlet port connected to the casing outlet port and first and second independent inlet ports, respectively, independently connected to the casing first and second inlet ports, the first valve inlet port being connected to the cylinders during the initial portion of the suction stroke of the pistons and the second valve inlet port being connected to the cylinders during the remainder of the suction stroke, means forming a fluid source at substantially atmospheric pressure connected to the casing first inlet port, a fluid motor having an inlet connected to the pump outlet and an outlet connected to the casing second inlet port, means for maintaining a supercharged pressure betweenthe motor outlet and the casing second inlet port for preventing pump cavitation by filling the cylinders at a supercharged pressure during the remainder of the suction stroke 0! the pistons, and means for exhausting excessive pressure fluid not needed by the cylinders.

12. In combination a fluid pump of the type having a casing housing a revolving cylinder barrel with a plurality of axially disposed cylinders having pistons reciprocable therein, and a valve having an outlet port and two independent inlet ports, the first inlet port being connected to the cylinders during the initial suction stroke of the pistons and the second of which is connected to the cylinders during the remainder of the suction stroke, a source of fluid at atmospheric pressure connected to the first inlet port, a fluid motor, separate conduit means connecting the pump outlet port to the motor inlet and the motor outlet to the pump second inlet port, and a pressure responsive relief valve connected in the conduit connecting the motor outlet to the pump second inlet port, said relief valve exhausting excessive pressure fluid not needed by the cylinders and also maintaining a predetermined supercharged pressure in the conduit for supercharging the pump during the remainder of the suction stroke thereby preventing cavitation.

HARLEY E. NIXON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Vickers et al Mar. 9, 1943 

